1. Field of the Invention
The invention relates to a brake torque plate and an installation method for fixedly attaching the torque plate to an axle or axle tube, and in particular to an installation method that minimizes or eliminates the gap between a bore or opening formed in the torque plate and the exterior surface of the axle tube, and that achieves perpendicularity of the inboard and outboard faces of the torque plate to the center line of the axle spindle/axle tube. More particularly, the present invention is directed to a torque plate having a bore or opening and a cut extending continuously between the torque plate peripheral edge and the bore, wherein the cut allows the torque plate bore to be temporarily expanded during installation of the torque plate on the axle. Upon successful slideable mounting of the torque plate about the axle tube, the cut is reduced or eliminated to create an interference fit between the torque plate and the axle tube, thereby reducing or eliminating the gap between the torque plate bore and the axle tube and ensuring perpendicularity between the torque plate faces and the axle centerline.
2. Background Art
Disc braking systems are well-known in the brake art and operate by squeezing a pair of opposing pads, via a caliper assembly, against a rotor, thereby creating friction between the contacting surfaces and enabling slowing and stopping of the vehicle on which the disc braking system is installed. Specifically, the caliper slides on guide pins which are incorporated into a caliper carrier. The caliper carrier typically is mounted on a plate, hereinafter referred to as a torque plate, that serves not only to resist torque generated during braking, but also to hold the caliper assembly square to the rotor to facilitate efficient braking.
Field and laboratory testing has shown that if the caliper, brake pads, and/or guide pins are not mounted and maintained square to the rotor, then premature failure of these components can occur. For example, uneven brake pad wear, guide pin binding that can cause chatter, and in some cases cracking of the rotor or caliper, are all problems that can occur.
To achieve the desired results of efficient brake operation in a disc braking system, it has become industry practice to provide means to mount and maintain the inboard and outboard faces or surfaces of the torque plate perpendicular to the center line of the axle spindle to a tolerance of less than 0.020 inches.
One means heretofore used for holding such a close tolerance has been to forge the torque plate and axle spindle as a single piece, finish machine the integral structure in one chucking, and then join the axle spindle/torque plate to the axle tube. Although this method of manufacture and assembly is very accurate, it is not practical for use with certain types of axle/suspension systems, such as the patented INTRAAX® axle/suspension system manufactured and sold by the assignee of the present invention, The Boler Company (U.S. Pat. No. 5,366,237). More particularly, an INTRAAX® axle/suspension system incorporates a trailing arm which completely surrounds the axle tube and is welded thereto around the entire circumference of the axle tube. Thus, during installation, this type of trailing arm must be slid over the axle tube before any brake hardware can be attached to the axle, making the one-piece torque plate/axle spindle structure and installation method impractical.
One known alternative to the one-piece axle spindle/torque plate structure, and in particular for applications where the axle/suspension system arm must be slid onto the axle tube prior to installation of the brake equipment, is a torque plate that has been fabricated independent of the axle spindle. The torque plate and axle spindle then are welded to the axle tube separately after installation of the suspension arm. In particular, the torque plate mating area on the axle tube is machined co-axial to the axle spindle center line, and the torque plate bore is pre-machined perpendicular to the plate faces. This process provides a slip fit of the torque plate on the axle tube to a tolerance of less than 0.015 inches between the torque plate and the axle tube before tacking and subsequent friction welding of the plate on the tube. However, due to the nature of such fabrication and assembly, there is a built-in variation in torque plate to spindle center line perpendicularity, as compared to the one-piece axle spindle/torque plate design described hereinabove. Thus, additional or secondary processing is required after welding the torque plate to the axle tube, such as by machining or straightening. Such secondary processing results in increased costs, which is undesirable.
In studying the causes of the variation in torque plate face to axle spindle center line perpendicularity, it has been proven that the gap between the torque plate and the axle tube has the greatest effect on perpendicularity. Therefore, a more effective design would minimize or eliminate the gap between the mating surfaces of the torque plate and the axle tube. Such a minimization or elimination of the gap could be accomplished by using a press or a shrink fit, but the machining tolerances required for such processes are even more costly than the secondary processing described immediately above. Thus, the need has existed for an efficient structure and method for installing a torque plate on an axle tube resulting in virtually no gap between the torque plate and the axle tube in order to maintain perpendicularity between the inboard and outboard faces of the torque plate and the axle spindle center line.
The present invention solves the above-noted problems through the addition of a continuous cut or opening in the torque plate which extends between the torque plate peripheral edge and the bore, thus allowing the torque plate bore to be temporarily expanded during installation of the torque plate on an axle tube and, upon installation, reduced to create an interference fit between the torque plate and the axle tube, thereby minimizing or eliminating the gap between the torque plate bore and the axle tube to ensure a perpendicular fit.